cookie小试刀—编写servlet利用Cookie保存上次访问该servlet的时间

最新推荐文章于 2023-10-16 19:16:46 发布

原创最新推荐文章于 2023-10-16 19:16:46 发布 · 1.8k 阅读

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#servlet #cookies #initialization #server #equals #constructor

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本文介绍了一种利用HTTP Cookie来记录用户登录时间的方法。通过设置和读取Cookie中的时间值，可以判断用户是否为首次登录，并显示用户的上次登录时间。

简单分析，由于http协议的无状态性不能保存数据，我们利用cookie保存用户上次登陆该servlet的时间，第一次登陆告诉是第一次登陆还没记录，（servlet中获取到的cookie值为空说明是第一次登陆这时设置上cookie的值保存这次登陆的时间）第二次及以后则显示上次的登陆时间（servlet中获取到的cookie值不为空，将cookie中的值显示即上次登录的时间）。

代码：

package com.zc.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class TestCookie2 extends HttpServlet {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	/**
	 * Constructor of the object.
	 */
	public TestCookie2() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 * 
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request
	 *            the request send by the client to the server
	 * @param response
	 *            the response send by the server to the client
	 * @throws ServletException
	 *             if an error occurred
	 * @throws IOException
	 *             if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doPost(request,response);
	}

	/**
	 * The doPost method of the servlet. <br>
	 * 
	 * This method is called when a form has its tag value method equals to
	 * post.
	 * 
	 * @param request
	 *            the request send by the client to the server
	 * @param response
	 *            the response send by the server to the client
	 * @throws ServletException
	 *             if an error occurred
	 * @throws IOException
	 *             if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		
		/*获取上册登陆的时间*/
		GregorianCalendar gc=new GregorianCalendar();
		
		String time=gc.get(Calendar.YEAR)+"-"+gc.get(Calendar.MONTH)+"-"+gc.get(Calendar.DATE)+"-"+gc.get(Calendar.HOUR)+":"+gc.get(Calendar.MINUTE)+":"+gc.get(Calendar.SECOND);//存放系统获取的时间
		if(gc.get(Calendar.AM_PM)==1){//判断上次登陆是上午还是下午
			time+="  PM";
		}else{
			time+="  AM";
		}
		
		Cookie timeCookie = new Cookie("lastTime",time);//存放上次登录时间的cookie
		timeCookie.setMaxAge(3600*24*365);//设置cookie的有效时间是一年
		
		response.addCookie(timeCookie);//添加时间cookie
		
		Cookie[] Cookies = request.getCookies();//获取所有cookie
		String lastTime=null;//存放上次登陆的时间
		for(int i=0;Cookies!=null&&i<Cookies.length;i++){
			if("lastTime".equals(Cookies[i].getName())){
				lastTime=Cookies[i].getValue();
				break;
			}
		}
		out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		if(lastTime==null){
			out.println("您是第一次登陆");
		}else{
			out.println("上次登陆的时间是："+lastTime);
		}
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 * 
	 * @throws ServletException
	 *             if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
	}

}

从上面的试验中可以看出cookie保存的总是上一次访问该网站时的信息。